This invention relates in general to a backlight system for a liquid crystal (LCD) or other electronic display and, in particular, to controlling the color and lumen level of a red-green-blue (RGB) light-emitting diode (LED) backlight and the sensor(s) that control(s) such a backlight.
Backlighting with white light generated by RGB LEDs is known to those skilled in the art. However, the characteristics of the LEDs vary with temperature, current, and aging. These characteristics also vary from one LED in a batch to another. Thus there is need for a feedback control to maintain within set limits the color and lumen level of such a backlighting system. For the feedback control to work satisfactorily, sensors must be placed properly to provide the necessary optical feedback.
The present invention provides apparatus and method for backlighting an electronic display with LEDs to control luminosity, radiometric power, and tristimulus levels by means of feedback control through a microprocessor, thereby maintaining the white backlight at substantially constant levels, which can be chosen by an operator.
In one embodiment of the invention, apparatus for backlighting an electronic display with white light comprises: a plurality of light-emitting diodes (LEDs), each of the LEDs effective for emitting light of a single color; at least one light source comprised of at least three of the LEDs arranged in a combination that produces white light; a light guide effective for illuminating the display with the white light; and circuitry effective for maintaining the white light at a substantially constant level of color and luminosity by controlling the at least one light source. This embodiment of the invention utilizes a method for backlighting an electronic display with white light comprising the steps of: driving a plurality of LEDs, each of the LEDs emitting light of a single color; combining light emitted from at least three of the LEDs to form white light; illuminating the display with the white light; and controlling the color and brightness of the white light by means of feedback circuitry.
In another embodiment of the invention there is provided apparatus for backlighting an electronic display with white light comprising means for driving a plurality of LEDs, each of the LEDs emitting light of a single color; means for combining light emitted from at least three of the LEDs to form white light; means for illuminating the display with the white light; means for controlling the color and brightness of the white light by feedback circuitry; and the means for controlling being subject to an operator""s direction. The present invention addresses one or more of these concerns.